First off good luck with your farm house. As to radiators I have purchased several old/used ones from salvage
places in Central NY. The trick is to lead test them before intalling them which is easy to do. There are lots of them around, one in Rochester called Old house parts, Ithica has one called Significant Elements. There used to be one in Homer NY my town but he is now at the Ithica place.
There is a big place in Conn. called United House Wrecking. All of these have web sites you can check out.
What is the name of the plumbing company in Cleveland?
Depends on the part of the country you live. Near Chicago, there are quite a few architectural salvage places.
You can probably get a few REALLY cheap by visiting the piles at your local scrap metal yard. They'll know these are valuable to you but on the other hand, these are untested and need some clean-up... plus they only paid scrap prices to send them to the steel mills.